Are you living "carbon neutral" – or better yet, "carbon negative"? Have you gone on a "carbon diet"? Are you shrinking your "carbon footprint" on the earth or aiming for a "net zero" lifestyle?

If so, you've got lots of company, including celebrities, sports teams, airlines, moviemakers, tour operators, and at least one college. They're all trying to make sure that they're removing at least as much carbon (in the form of carbon dioxide, or CO2) from the atmosphere as they add from heating their homes or businesses or traveling by car or airplane.

Americans have been shutting off lights, stuffing insulation into attics, and carpooling to save gas at least since President Jimmy Carter pulled on his cardigan and talked to the nation about saving energy nearly three decades ago.

In the 21st century, though, the conservation message has changed: While fossil fuels such as oil and coal continue to dwindle and become more expensive, burning them now has an almost certain link to the warming of the planet's atmosphere, creating a rapidly changing climate that could wreak havoc.

People are eager to help, and going "carbon neutral" has become a popular answer. The New Oxford American Dictionary recently proclaimed "carbon neutral" as its Word of the Year for 2006. "The increasing use of the word 'carbon neutral' reflects not just the greening of our culture, but the greening of our language," says editor in chief Erin McKean. "When you see first-graders trying to make their classrooms 'carbon neutral,' you know the word has become mainstream."

Polls back up the editors' choice. Americans now say climate change is the country's most pressing environmental problem, according to a recent survey from the Massachusetts Institute of Technology. Just three years ago, it ranked only sixth on a list of 10 environmental concerns.

Becoming "carbon neutral" involves two steps, environmentalists point out. The first is to reduce carbon emissions through familiar conservation measures: replacing incandescent light bulbs with fluorescent bulbs, using public transit, and so forth. Many online "carbon calculators" help individuals or businesses assess how much carbon they are emitting.

But that only reduces their carbon emissions. To get to zero, they'll need to buy "carbon offsets" by sending money to projects that replace fossil fuels with renewable energy sources, such as solar or wind-power generators, or to projects that remove carbon dioxide from the air, such as tree farms.

For example, a new business-class airline, Silverjet, plans to add a levy of about $26 to its transatlantic fares that will be sent to carbon-reducing projects to offset the carbon burned during the flight.

But some environmentalists worry that the idea of going "carbon neutral" could be detrimental if it leads to people only buying offsets and not changing their lifestyles.

"The concept of carbon neutrality is great. But it's one thing for people to do things to reduce their carbon emissions in their own lives; it's another thing for people to buy credits or offsets counting on someone else to clean up their act," says Dan Becker, director of the Sierra Club's global warming project. "It would be bad if it has the impact of creating sort of 'papal indulgences' that people feel that they're allowed to buy a gas-guzzling SUV or otherwise pollute in ways that they could avoid because they can pay someone else to plant some trees in Guatemala."

Offsets alone aren't going to achieve the greenhouse-gas reductions that are needed, adds Charles Miller, a spokesman for the Environmental Defense Fund in Washington, D.C. "We've got to learn to use energy more efficiently, and we've got to reduce our consumption of energy."

It's a dangerous way to "let people off the hook," agrees Mary Rosenblum, an author who writes science-based novels set in the near future. In her forthcoming book, "Water Rights," the US is faced with desertification from a vastly changed climate. "It's what our future will probably look like if we don't do anything about it," says Ms. Rosenblum, who lives near Portland, Ore.

"If you can drive three SUVs and charge up a couple of hundred bucks [of carbon offsets] on your Visa and then think, 'OK, I've done my share,' we're not going to change anything," she says.

Other environmentalists say influencing what China and India do about their growing carbon emissions will be much more significant than the feel-good efforts of Americans to become carbon neutral.

But some argue that even though the offset programs may be of dubious value, little more than paying lip service to cutting carbon, they still serve a valuable function in educating the public.

It's true that Americans can pay for their "carbon sins" with a relatively small amount of money, says Michele Bowman, a futurist and managing director of Global Foresight Associates in Waltham, Mass. But more important, they'll start to realize exactly what goes into creating carbon emissions and how they're offset, she says. "And that in turn is going to start to change behavior."

Ms. Bowman arranged to have the Pop!Tech conference in Camden, Maine, a gathering of thought leaders interested in how science and technology are shaping the future, go "carbon negative," offsetting its carbon emissions by twice the amount used by the 530 participants (about 800 tons of carbon) while at the October conference and in their travel to and from it. Pop!Tech invested in solar generators that will power villages in the African country of Benin through a group called the Solar Electric Light Fund (www.self.org)

On a grander scale, the Kyoto Protocol has committed countries to reducing greenhouse gas emissions. It has also stimulated a growing worldwide market for carbon-emission permits that are bought and sold between businesses. As a result, some observers say, awareness of the need to cut carbon emissions is higher in participating countries such as Canada and Britain than in the US, which has not signed onto the deal.

But Americans are beginning to catch up, say those involved in the carbon-reduction movement. One big influence has been the "An Inconvenient Truth," the documentary that examines former Vice President Al Gore's crusade against global warming. The film was released in theaters earlier this year and on DVD last month.

"The past year has been tremendous," says Billy Connelly, part owner and marketing director of Native Energy of Charlotte, Vt., which sells carbon offsets. The level of public understanding about carbon emissions is much greater now than two to four years ago when the majority native American-owned company was just starting out.

"It's due in no small part to Mr. Gore's film," he says.

Native Energy invests in solar, wind, and biomass energy-generating projects that aim to "push coal-fired and gas-fired energy off the [electric] grid," Mr. Connelly says. In one native village in Alaska, he says, a wind turbine is replacing expensive diesel fuel that had to be flown in to make electricity.

The villagers have seen firsthand the results of global warming, he says. "The permafrost is literally melting beneath them."

Individuals who have bought carbon offsets from Native Energy include the Middlebury (Vt.) College ski team, Ben & Jerry's ice cream, Clif Bar energy bars, and the Canadian alternative rock band Barenaked Ladies. The Dave Matthews Band has bought enough offsets, Connelly says, to make up for the carbon the group has emitted during its entire 15 years of touring.

Meanwhile, the College of the Atlantic in Bar Harbor, Maine, is proclaiming itself to be the first such institution pledged to be carbon neutral. The college plans to offset all student and faculty commuting to campus and any other carbon emissions "caused by our existence," says college president David Hales.

The school's fleet of boats, for example, has been converted to burn only renewable biofuels.

Students are heavily involved on committees now researching how to determine the size of the college's "carbon footprint" and how to best buy carbon offsets. Whatever offsets are purchased must show that the projects they support have "quantifiable, verifiable" results in reducing carbon emissions, Mr. Hales says.

Trustees, alumni, parents, and donors back the carbon-neutral initiative, he adds. The school's pledge follows other environmental moves at the college. It already buys all of its electricity from a wind- powered source and held a "zero-waste" graduation ceremony last year.

Kenyan environmentalist Wangari Maathai, who won a 2004 Nobel Peace Prize, recently urged what might be the grandest plan yet to offset carbon emissions at last month's international meeting on climate change in Nairobi, Kenya. Ms. Maathai proposed that the world's citizens commit to planting 1 billion trees, which would absorb about 250 million tons of the carbon dioxide now warming the atmosphere.